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UNIVERSITY OF NEBRASKA-LINCOLN
WINTER 2007-08

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Alumni Tips

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Bridges: Two Cities, Two Perspectives

By Brian Nielson

Bike Lanes: Making Space for Safety

By Natasha Richardson

Engineering the Downhill Bike

By Matt Buxton

Alumni Tips: Mindy Yechout

By Hannah Peterson

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Bridges: Two Cities Two Perspectives

The engineering world took notice when the Interstate 35W Bridge in Minneapolis, Minn., collapsed
during rush hour traffic on Aug. 1, 2007, killing 13 people. Engineers in Nebraska have been working to design new bridges that will not fail in such a way.

Harris Overpass

There has been some type of bridge in the location of the current Harris Overpass in Lincoln since the 1880s. The current one was built in 1955. This bridge was designed to have a 50-year life span. Sometime around 1999-2001, the sufficiency rating of the bridge dropped below 50 percent, qualifying it for federal replacement funds. The design work for the new Harris Overpass began in 2004.

Minneapolis’ I-35W Bridge was said to have “non-redundant” supports. That means that if one part went down, the rest of the bridge would also fail.

Today’s Harris Overpass, on the other hand, has redundant supports. Each support is three piers wide. Kris Humphrey, the design project manager for the Harris Overpass project, said that a train derailment under the overpass in the 1980s took out only one of the piers on a side, leaving two across to support the road. The road on that side lowered a few feet, but the bridge did not completely collapse, making it much safer than non redundant bridges.

“This is one reason we are replacing the bridge all at once,” Humphrey said. “If we only did one side at a time, we could not put three piers across and the bridge would no longer be redundant.”

All of today’s new bridges in Nebraska use nuts and bolts, rather than the rivets used when the I-35W Bridge was built in Minneapolis in 1967.

More heavy girders will be added to the new bridge. Humphrey said the new bridge is designed to have a life span of 75 to 100 years.

Currently, the bridge features bridge will only have two expansion joints. Humphrey said the reason for this is that better materials and more testing have been developed since the bridge was built in the 1950s.

“One reason that the bridge is in need of replacement now is that snow and salt got into the expansion joints and rusted out the trusses underneath,” Humphrey said. “So we would like to be able to get by with less expansion joints.” Today’s bridge is 1,867 feet long, and the new length will be 1,886 feet. While the current bridge has 28 concrete piers, the new bridge is designed to have 14. The sidewalk on the new bridge will be 4 feet wider than the current one. A flatter and wider median will be built on the new bridge.

Many safety concerns have been expressed at the west touchdown of the bridge at 3rd and O streets. The new intersection will only allow for right turns off the bridge onto 3rd Street. A raised median will extend through that intersection. For the safety and pleasure of pedestrians under the overpass in the Haymarket area, there will be corrugated steel ceilings underneath the girders to prevent pigeons from roosting there and making a mess.

Humphrey said the city also looked into installing a new anti-icing system for the roads on the overpass. However, these new technologies still have their problems, so such a system will not be installed. Instead, the city will install dynamic message signs that can detect ice on the streets and alert drivers, as well as send Amber Alerts and other information.

Construction on the O Street frontage road began in October 2007. The overpass itself shut down on Nov. 12th to begin construction. Construction is projected to last one year. Plans were also made to accommodate the possible new arena and convention center planned west of the Haymarket. Humphrey says the project is unique because it involves two railroad entities, it is adjacent to the Haymarket and it ties together east and west Lincoln.

West Dodge Expressway

Unlike the Harris Overpass, the West Dodge Project in Omaha involves two completely new bridges.

The new expressway bridges begin just east of 108th Street and end at about 131st Street. One bridge sits on each side of the road hanging out over the at-grade West Dodge Road. The bridges are one mile long and 40 feet high. Three lanes of traffic flow on the westbound bridge and three lanes flow on the eastbound bridge. For example, traffic heading west can choose to take the expressway bridge if it does not have a destination of
120th Street, 114th Street or the Old Mill area. Traffic that does have a destination on one of these streets can take the existing groundlevel road that runs underneath the expressway bridges. The bridge at the 120th Street intersection was removed completely and is now a ground-level intersection.

Karl Burns, the public relations project manager for the West Dodge Project, said the bridge was designed for a standard 80-year life span. The concrete used in the abutments was the standard 47BD (bridge design) mix of 30 percent limestone and 70 percent gravel, used by the Nebraska Department of Roads on most bridges.

Burns said the expressway bridges went through the normal inspection procedures as they were being constructed.

He said, “We start at the foot and test the piling for bearing. Then we test the concrete for the required pounds per square inch.”

Burns said NDOR even had inspectors at the plant. NDOR inspected the rebar as it was shipped. They tested the samples through break tests.

Construction began in 2003 and the bridge opened on July 27, 2006. At the end of 2007, the final detail work was done. This included putting in decorative stone and pavers, laying sod and painting the road markings. Construction was completed an impressive one year ahead of schedule. Incentive money was tied to getting the project done on time, but Burns credits the cooperation between Hawkins Construction Company, the engineering and consulting firm HDR and NDOR as a key in the early completion of the project.

About 80,000 vehicles per day use West Dodge Road.

“We have recorded that 70 to 75 percent of the traffic takes the expressway bridges, as expected,” Burns said.

He added that the number could soon go up to 80 percent.

Burns said, “It was a good project, and I was glad to be associated with it.”

 

     

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